Chemo-mechanical timer

ABSTRACT

A chemical-mechanical timing device for automatically releasing a retained member at the end of a predetermined period of time. The apparatus includes a chemical pellet, and associated rivet, which are kept dry until the timing action is to begin. Then the pellet is exposed to the moisture in the ambient air, or water for underwater devices, and a chemical action is initiated between the pellet and rivet. The rivet is partially consumed and weakened to the point of releasing a retained member.

gnited States Patent [72], Inventor Keith D. Anderson Upland, Calif. 12l 1 Appl, No. 827,395 1221 Filed May 23. 1969 [45 Patented Aug. 17. 1971173 l Assignee The United States of America as represented by theSecretary of the Army i541 CHEMO-MECHANICALTIMER 5 Claims, 2 DrawingFigs.

15 ,1 58/111, 23/2529. 51 604i 1/02 [501 FieldotSearch. zztlrs; 9/317,323; 23/252 11.230 C'.58/l R l 56] References Cited UNITED STATESPATENTS 2,d37,534.12ll943 Barber .Q

3,018,611 [/1962 Biritz I t v H 58/1 R 3.520.124 7/1970 Myers H 58/111FORElGN PATENTS 540,583 5/1957 Canada 58/1 R Primary Examiner- Morris 0Wolk Assistant Examiner Barry S. Richman Auorneys- Harry M. Saragovitz,Edward J. Kelly, Herbert Berl and Robert P Gibson ABSTRACT: Achemical-mechanical timing device for automatically releasing a retainedmember at the end of a predetermined period of time. The apparatusincludes a chemical pellet, and associated rivet, which are kept dryuntil the timing action is to begin. Then the pellet is exposed to themoisture in the ambient air, or water for underwater devices, and achemical action is initiated between the pellet and'rivet. The rivet ispartially consumed and weakened to the point of releasing a retainedmember.

ft'scret e' gap I t f e we n rzve and BRIEF SUMMARY dropped into a bodyof water.

The present invention performs such functions. The moisture entering theapparatus initiates a reaction in a pellet, of a corrosive salt forexample. The corrosive salt attacks an element of the apparatus, such asan aluminum rivet for example. The element is progressively weakened tothe point where it can no longer restrain a part and lets go."

It is an object of this invention to provide a chemicalmechanical timingdevice as set out above which is simple in operation, inexpensive tomass-produce, reliable in operation, small insize and light in weight.Such device has no springs or such energy sources, or gear trains orsimilar mechanical parts. In the drawing:

FIG. I is a view of the invention in partial cross section;

FIG. 2 is an exploded view of the invention.

Body member I is provided with a recess 2 to receive the basiccomponents of the invention. The basic parts, including rivet 4, hold amechanical coupling or securing member 3 fixed to body I. The componentscomprise a rivet or other securing device 4, a pellet 5, a membrane 6and a retainer 7 having moisture access holes 8 therein. Moisture fromthe surrounding environment enters through holes 8 in retainer 7,penetrates membrane 6, and softens or dissolves pellet 5. Pellet 5, ofcupric chloride salt for example, is corrosive with respect to rivet 4which may be made of an aluminum alloy for example.

OPERATION When the quantity of water or vapor entering the cavity hasreached a critical value the pellet constituents initiate a gas phasechemical reaction with the metal rivet. The gas phase reaction formsreaction products which are very hygroscopic, hence a small bubble isformed on the rivet head. The bubble grows until it closes the gapbetween the rivet head and the pellet. When the bubble attaches to thepellet the reaction rate increases markedly and the rivet is consumed orweakened to the point that member 3 breaks away.

The basic device can be tailored for a broad range of applicationsandtime delay periods. The water vapor permeability properties of membrane6, membrane thickness, and membrane area, provide one set of designvariables which tailor the time delay period. The width of the airgapbetween the pellet and rivet head provides another time delay designvariable.

The size of the rivet head affects the time required for it to beconsumed to release-member 3.

The storage environment may consist of a simple, sealed, impermeable,bag or container and an adequate amount of desiccant. it is alsopossible, depending on pellet formulation, to store the timer in afrozen state with the unit coming to life after thawing, or to store thetimer in a moist or wet environment with the chemical action occurringas the timer dries out.

Inasmuch as the time delay action results from a water or vaporinduction period, followed by a gas phase chemical reaction, and then aliquid phase chemical reaction, the effect of variations inenvironmental humidity level on the time delay period is reduced.

To give examples of materials which may be used, the pellet may consistof a suitable corrosive salt, e.g. cupric chloride,

ferric chloride, etc., with inert f llers such as silica flour to insurepellet integrity and to provide adequate granular surface area, watersoluble binders, and desiccant additives.

lclaim: 1

l. Chemical-mechanical timer apparatus comprising a body member, amechanical coupling member, a securing device having a portion adaptedto be chemically attacked securing said coupling member to saidbody'member, means to weaken said securing device during a period oftime to permit separa tion of said body member and said coupling member,said means comprising a chemical material adapted to be actuated upon achange of environmental moisture conditions, said chemical materialcomprising a corrosive salt soluble in said environmental moisture andin proximity to said securing device such that said corrosive salt, uponactuation by environmental moisture, chemically attacks said securingdevice and weakens same during said period of time, at the end of whichsaid securing device structurally fails and releases said mechanicalcoupling member.

2. Apparatus as in claim 1 wherein said chemical material furthercomprises an inert filler and a moisture soluble binder.

3. Apparatus as in claim 2 wherein said chemical material furthercomprises a desiccant additive.

4. Apparatus as in claim 1 wherein said securing device comprises arivet with a head adjacent to said corrosive salt.

5. Apparatus as in claim 4 wherein said rivet comprises an aluminumalloy.

2. Apparatus as in claim 1 wherein said chemical material furthercomprises an inert filler and a moisture soluble binder.
 3. Apparatus asin claim 2 wherein said chemical material further comprises a desiccantadditive.
 4. Apparatus as in claim 1 wherein said securing devicecomprises a rivet with a head adjacent to said corrosive salt. 5.Apparatus as in claim 4 wherein said rivet comprises an aluminum alloy.